SD may refer to:
Military and weaponry Smith & Wesson SD, a line of pistol (first made 2010) SD radar, an early US Navy radar system Southern Cross Decoration (SD), a South African military award
Organisations Political parties Democratic Left (Italy) (2007–2010; ) Social Democrats (Slovenia) (founded 1993) Solidarity (Brazil) (founded 2012) Democratic Party (Poland) (founded 1937; ) Sweden Democrats (founded 1988) Swiss Democrats, Switzerland (renamed 1990; ) Serbian Right (founded 2018; )
Other organisations Sicherheitsdienst, Nazi intelligence service (1931–1945) Sisters of the Destitute, a Syro-Malabar Catholic order (founded 1927) Sudan Airways (founded 1946; IATA:SD)
Places Sudan (ISO 3166 country code:SD) A common abbreviation for the U.S. city of San Diego, California and the San Diego Padres—the city's Major League Baseball team Shandong, a province of China South Dakota, a US state Eswatini (formerly Swaziland; SD on vehicle plates)
Science and technology Astronomy Subdwarf, a class of star Surface detector, of cosmic rays at the Pierre Auger Observatory
Electronics and computing SD card (Secure Digital), a flash memory card format Software Distributor, an HP-UX system Standard-definition television Super Density Disc, an optical disc format Stable Diffusion, a text-to-image generator
Mathematics sd (elliptic function), one of Jacobi's elliptic functions Standard deviation (SD), a statistical measure of variation
Medicine Spasmodic dysphonia, a voice disorder Stable disease, a RECIST chemotherapy outcome
Other uses in science and technology Segregation distorter, a selfish genetic element which biases its own genetic transmission Service design, holistic design of service experience Spiral Dynamics, a model of individual and societal development Storm Data, a US meteorological journal System dynamics, of nonlinear systems
Other uses Sekolah Dasar, term for primary school in Indonesia Sindhi language (ISO 639-1 code: sd) sine die, Latin, undated (literally without a day) Split decision, in full-contact combat sports Super D (cycling), a class of mountain bike race Super deformed, an art style
See also SD1 (disambiguation)